It is a fascinating question: why are we all different? What choices are involved in the different things we all choose to learn, and what lack of choice is there in the things we have no choice but to learn. And when are those choices made?
Locke thought we were born with nothing imprinted on our brains whatsoever, so if you think like him you may assume those early unknown influences are the ones that dictate if you are good at mathematics or literature. My mother grew up to know she was a poet and it cannot be a coincidence that during my grandmother’s pregnancy with her, my grandfather recited endless reams of poetry he had learned in Reform School and beyond. His love was imparted to his daughter.
There may also be innate skills which is why some people study a career to please their parents but all their lives really want to be painters. In actual fact you might have to study millions of people and discuss their lives in detail to have the full range of answers. The fact remains that brains are different for all their similarity and something obvious to you will be difficult for me to grasp.
And perhaps we don’t need an answer, except to allow people to be who they are without let-or-hindrance as long as they harm no one else. Perhaps we are all different because the hardest thing to learn is to allow difference to flourish.